Field of the Invention and Related Art Statement
This invention relates to an automatic light adjusting system for an endoscope using an externally fitted camera wherein, even in case the image forming area varies, a proper light amount controlling function will be obtained.
Recently, there has come to be extensively used an endoscope (fiberscope) whereby an affected part or the like within a body cavity can be observed or treated to be cured by using a treating tool as required by inserting an elongated insertable part into the body cavity without requiring an incision.
In the observation or diagnosis with the above mentioned endoscope, in order to know whether the disease has recovered or not, it is necessary to record the state. In such case, often an externally fitted camera using such solid state imaging device as a CCD (charge coupled device) for the imaging means is fitted so that an optical image by a fiberscope may be converted to an electric video signal to be recorded by a VTR or the like or a photographic camera is fitted to take a photograph.
In some fiberscopes, the objective optical system is formed of a zooming optical system so that the magnification in the observation may be varied.
In the above mentioned zooming optical system, if the magnification is varied, the light amount will vary on the observed surface or photographed surface and will become unfavorable to recording or photographing.
Therefore, the present applicant has suggested in the patent gazette of Japanese patent laid open No. 211113/1982 an endoscope apparatus wherein the light amount is adjusted as operatively connected with the magnification variation of a zooming optical system to keep constant the incident light amount on the observed surface or photographed surface so that photographing or the like may be made with a proper exposure amount by utilizing this incident light amount.
This related art example is of a mechanism in which the light amount must be controlled as operatively connected with a zooming optical system. It is necessary to provide each fiberscope with this mechanism.
Now, in some case, it is desired to fit an externally fitted camera to not only a fiberscope of a zooming optical system but also a fiberscope of no zooming optical system so that a video image displayed in a monitor may be recorded by a VTR or the like.
In such case, there are various fiberscopes of image guide fiber bundles of large and small outside diameters in response to the uses.
For example, in FIG. 1A, (a) shows an optical image range DA of a fiber bundle within an imaging range L in case an externally fitted camera is fitted to a fiber scope having a large diameter image guide and (b) shows the video signal in such case.
On the other hand, with a fiberscope having a small diameter image guide, in the same manner, they are as shown in FIG. 1B.
In the case of fitting the above mentioned externally fitted camera, there is a prior art example wherein the illuminating light amount is adjusted to be on a proper level by an average value level, of a video signal. However, as shown in the above mentioned FIGS. 1A and 1B, the optical image range (picture image range of image area) formed on the imaging surface of the camera varies with the diameter of the image guide of the fiber scope and therefore the average value levels of the image signals fluctuate respectively as in VA and VB.
That is to say, in FIG. 1A, even if the rate of the range of the video image or picture image part to the range of the effective imaging range in the lateral direction is large and the amplitude of the video signal itself is small, the average level VA of the video signal will be large but, in FIG. 1B, unless the amplitude of the video signal itself is large, the average level VB of the video signal will become small. That is to say, due to the size of the image area, for example, a level difference .DELTA. will be produced between them.
Therefore, even if an automatic light adjusting function automatically adjusting the illuminating light amount by the average level of a video signal is provided, in the method of the prior art example, if it is used for a fiberscope or the like different in the diameter of the image guide, the average level will also vary depending on the diameter and the illuminating light amount has not been able to be adjusted to a proper value. Therefore, the contrast of the picture image displayed on the monitor picture surface will be too bright or too dark. In the case of diagnosing with a monitor picture image, it will be likely to be difficult to well discriminate the affected part or the like.